Dear Editor:

The recent article “Extractable Arsenic from Activated Carbon Drinking Water Filters” in the November, 2004 edition of WC&P raised several points relative to the testing of water filters and conclusions drawn on health effects of arsenic. NSF has more than 30 years experience with the development of this Standard, and in the testing of such products. Based upon this experience, we have a few comments to offer in response to the article.

Source of the NSF Standards
While some may be very familiar with how the NSF/ANSI Standards are developed, I expect many are not. To review briefly, NSF International is accredited by the American National Standards Institute (ANSI) to develop consensus based American National Standards. The purpose of ANSI is to establish a single, broadly accepted and agreed upon, national method of evaluating products. The ANSI accredited, consensus standards process utilized by NSF involves an expert committee comprised of an equal balance of stakeholders from the regulatory, manufacturing, and user communities. There are approximately 33 experts in total, including representatives from USEPA, Health Canada, State regulatory agencies, certification bodies and many others. This collective body, often through the advice and input of many other stakeholders that participate through various task groups, decide upon the content of the standards.

The work produced by this committee is reviewed by yet another, the NSF Council of Public Health Consultants (CPHC). This is a peer group of regulatory experts who approve all standards prior to adoption as NSF/ANSI Standards. The CPHC includes representatives from USEPA, State regulatory agencies, the Centers for Disease Control, and others. There are no industry representatives on this committee. As the name implies, their focus is on the public health protection offered by the standards.

As American National Standards, there is still another step that takes place outside of the NSF committee process and allows for public review and comment. Comments are provided back to the NSF committees for review and consideration.

Collectively, this overall process ensures broad stakeholder participation to achieve the most technically sound and widely accepted standard possible. Once adopted, however, no standard remains stagnant. All are reviewed and revised through the same process with frequent task group meetings and biannual expert committee meetings.

Appropriateness of Extraction Test Procedure
The extraction test procedure of NSF/ANSI Standard 42, as referenced in the article, has evolved over the years. All versions have been highly conservative in terms of public health protection, including the following:

  • All have consistently tested the first product water delivered by the system following the manufacturer’s recommended conditioning and after a minimum dwell time of not less than 24 hours;
  • All have used exposure water intended to be aggressive in terms of drawing out extractable contaminants from the wetted materials;

Further examples of the comprehensive, conservative nature of this Standard include the following:

  • Systems with adsorptive or absorptive media are tested both with and without the media. This ensures that any contaminants produced by the non-media components of the system which may be reduced by the media are properly identified;
  • Analysis of the extractant water comprises a large, standard battery of parameters, and an additional battery of formulation dependent parameters;
  • No normalization of the resulting values is allowed; and
  • The pass/fail criteria are based on the USEPA National Primary Drinking Water Regulations Maximum Contaminant Levels (MCLs) where they exist, and on the maximum permissible concentration of a contaminant in drinking water as established by a recognized regulatory authority, such as the USEPA or Health Canada, or by an NSF risk assessment when no established value exists.

Significance to Public Health
The authors take the position that the pass/fail criteria of NSF/ANSI Standard 42 for arsenic could still be exposing consumers to unacceptable levels. The authors are correct that NSF/ANSI Standard 42 has a maximum contaminant concentration for arsenic of 10 parts per billion (ppb), consistent with the new MCL set by the USEPA. The authors are also correct that the maximum contaminant level goal is 0 ppb. The simple conclusion drawn is that less would be desirable. However, it is important to emphasize that these MCLs are based on chronic, life-time exposures, and the nature of arsenic leaching from carbon over time is for rapid decline in the initial level rather than a sustained, chronic leaching.

What the author’s research demonstrated, and what is the design of the Standard, is that the first product water collected represents the most extreme condition of arsenic leaching from the system. The two units tested for “simulated aging” were both identified as undersink type systems. Conservatively, these would be expected to have a minimum rated capacity of 300 gallons. The data showed that at 40 Liters, or approximately 10 gallons, both filters were demonstrating arsenic levels of <1 ppb, and continuing on a downward trend. In addition, of the five products tested against the normal extraction testing under NSF/ANSI Standard 42, these two systems demonstrated the highest levels of arsenic.

When factoring in the reduced leaching of arsenic over time, and the conservative characteristics of the extraction test method, it is more likely that the exposure from products tested and certified to be in compliance with the Standard have a predominance of exposure much closer to the desired 0 ppb. We agree with the authors that a conclusive measure of this would require further testing, but the preliminary data strongly supports this outcome.

Further, the authors do not give credit to the many benefits these products provide in terms of reducing other organic and inorganic contaminants of concern, including carcinogens. Carbon based treatment products are common and readily available in the market for many reasons, one of which is the cost-effective, public health benefits they bring the consumer.

Future Work
NSF would welcome discussions with the authors regarding future work in this area, and invite their involvement with the standard’s development process. The NSF/ANSI Standards are dynamic and meetings occur regularly to review and expand upon them. New research and contributors are always welcome.

Thank you for the opportunity to comment.


Thomas J. Bruursema
General Manager, Drinking Water Treatment Unit Program
NSF International


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